Multi-layer, composite current collectors may be used, for example, in electrodes for ultracapacitors, also known as electrochemical double layer capacitors (“EDLCs”), which are electrochemical devices that have highly reversible charge-storage and charge-delivery processes per unit volume and unit weight as compared to batteries. Ultracapacitors may also be desirable because they may not contain hazardous or toxic materials and, therefore, may be easy to dispose of. Additionally, they may be utilized in large temperature ranges, and they have demonstrated cycle lives in excess of 500,000 cycles. Ultracapacitors may be used in a broad spectrum of applications such as, for example, fail-safe positioning in case of power failures, portable electronics, and electric vehicles.
In an ultracapacitor, electrons conduct electricity to and from each of the two electrodes through an external circuit, while ions flow in between the electrodes. Many intrinsic and extrinsic components of an ultracapacitor device contribute to the overall equivalent series resistance, including the electrode resistance at the interface between the active material and the current collector. Reduction in the electrode interfacial resistance may reduce the equivalent series resistance and increase the power density for the ultracapacitor device. Incompatibility among elements comprising an intermediary coating at the current collector interface may, however, cause difficulties in making multi-layer current collectors and ultracapacitor electrodes.
Thus, there exists a need for methods of making multi-layer current collectors with the desired microstructure, thickness and composition. There further exists a need for methods of making multi-layer current collectors and ultracapacitor electrodes that reduce the electrode interfacial resistance and improve the performance of the ultracapacitor. There is also a need for methods of making multi-layer current collectors and ultracapacitor electrodes in a cost effective manner, e.g., reducing material costs and/or manufacturing time.